(a) Field of the Invention
The present invention relates to a method of constructing a resource allocation map for a mobile communication system. More particularly, the present invention relates to a method of constructing a resource allocation map for an OFDMA mobile communication system in a case where a localized resource block (localized RB) and a distributed resource block (distributed RB) need to be simultaneously allocated in regards to a radio resource allocated in a previous frame or reserved with a fixed allocation.
(b) Description of the Related Art
An orthogonal frequency division multiplexing (hereinafter, referred to as “OFDM”) method is a method in which after high-speed serial signals are separated into low-speed parallel signals, the low-speed parallel signals are modulated with an orthogonal sub-carrier, and the modulated low-speed parallel signals are transmitted and received. Further, a transmission terminal maintains orthogonality between carriers by using a simple method, such as guard interval insertion. As a result, a complicated equalizer or a rake receiver in a DS_CDMA (direct sequence-code division multiple access) method becomes unnecessary in a reception terminal.
Since an orthogonal frequency division multiple access (hereinafter, referred to as “OFDMA”) method has excellent characteristics, the OFDMA method has been adopted as a standard modulation method in digital broadcasting, a wireless LAN such as IEEE 802.11a or HIPERLAN, and a fixed broadband wireless access such as IEEE 802.16. The OFDMA method has been examined as one of applicable technologies of a modulation and demodulation/multiple access method even in a UMTS (universal mobile telecommunications system).
Currently, various OFDM-based multiple access methods are actively being researched. Among them, the OFDMA method has been examined and researched as a candidate technology for achieving next generation mobile communication in which a user request for high-speed multimedia services or the like is rapidly increasing. The OFDMA method is a two-dimensional access method that couples a time division access technology and a frequency division access technology.
FIG. 1 is a diagram illustrating a structure of a data frame in an OFDM/OFDMA wireless communication system according to the prior art.
In FIG. 1, the horizontal axis indicates a time axis that is displayed in a unit of a symbol, and a vertical axis indicates a frequency axis that is displayed in a unit of a sub-channel. The sub-channel means collection of a plurality of sub-carriers. Specifically, in an OFDMA physical layer, active sub-carriers are divided into groups, and each sub-carrier group is transmitted to a different reception terminal. A sub-carrier group that is transmitted to one reception terminal is referred to as a sub-channel. The sub-carriers that form each sub-channel may be adjacent to one another or spaced apart from one another at equivalent intervals. At this time, a distributed sub-channel that is composed of distributed sub-carriers is referred to as a distributed resource block (hereinafter referred to as “distributed RB”), and a localized sub-channel that is composed of neighboring sub-carriers is referred to as a localized resource block (hereinafter referred to as “localized RB”). That is, when sub-carriers that belong to a resource block (hereinafter referred to as “RB”) are distributed on a frequency axis, the corresponding RB is referred to as a distributed RB, and when the sub-carriers are adjacent to one another, the corresponding RB is referred to as a localized RB.
In this case, the RB is a minimal radio resource unit that divides a radio resource used when transmitting downlink data and uplink data, and each RB is composed of a plurality of sub-carriers on a frequency axis and one or more symbols on a time axis.
Generally, due to multipath fading, in a movement radio channel, a specific band has a high channel gain on a frequency axis, while another band has a low channel gain. That is, the movement radio channel has a frequency selective fading characteristic. When a user walks to move, that is, when a movement speed of a terminal is low, since a channel gain slowly varies in each band, the terminal selects a specific band that has a relatively large channel gain and informs a base station of the selected band, and the base station is allowed to transmit data in a transmission method where a data rate is high in the corresponding specific band, thereby obtaining a frequency selective scheduling gain. In this case, it is required that a radio resource belonging to the band selected by the terminal is not distributed on a frequency axis but exists in the corresponding band. For this reason, the base station allocates the radio resource to the corresponding terminal by using the localized RB.
When a mobile terminal moves at a high speed and thus a channel quickly varies or there is no information for the band selected by the mobile terminal, frequency selective scheduling cannot be used. In this case, in order to obtain frequency diversity, the base station allocates the distributed RB composed of sub-carriers distributed from the side of the frequency to a mobile terminal.
The base station uses a map to inform each mobile terminal of information for the radio resource allocated in the above-described manner. That is, in order to inform each mobile terminal of the information for the radio resource allocated to each mobile terminal, the base station constructs the map including information for an ID corresponding to a mobile terminal to which the radio resource is allocated, a location of the allocated radio resource, and a transmission method to be used in the allocated radio resource.
Meanwhile, in order to effectively transmit the map, the map may be transmitted in a state where a different modulation and coding scheme is applied to the map. In this case, radio resource allocation information is transmitted through sub-maps having different modulation and coding schemes. A main map includes information for the location of the radio resource used when transmitting each sub-map and information for the used modulation and coding scheme, and each sub-map includes radio resource allocation information for the mobile terminal. Hereinafter, the main map is referred to as a mother map, and the sub-map is referred to as a child map. As for the radio resource used for transmitting the map, a radio resource is notified through a broadcasting channel, or a generally known fixed radio resource is allocated. Accordingly, a method of allocating a radio resource for transmitting the map is not described below.
FIG. 2 shows a method of allocating a radio resource composed of twenty-four localized RBs to three mobile terminals. According to this method, the base station informs each terminal of radio resource allocation information by using a bit-map method.
Generally, a frequency bandwidth that has a high channel gain with respect to each mobile terminal according to a frequency selective channel characteristic of each mobile terminal may be focused on an arbitrary portion in an entire band or distributed partially in the entire band. In this case, since the distributed frequency band may be selected and used, a bit-map that can inform the locations of allocated RBs is used.
As shown in FIG. 2, when the bit-map method is used, the number of bits needed when transmitting information of a radio resource allocated to each terminal is needed by the number of RBs in the entire radio resource, for example, 24 bits when the entire radio resource is composed of twenty-four RBs.
Further, in order to represent an RB that is allocated to a corresponding terminal, a corresponding bit is set to 1, and in order to represent a RB that is not allocated to the corresponding terminal, a corresponding bit is set to 0. For example, when RBs allocated to a terminal #1 are 2 and 14, the second and fourteenth bits become 1, and the other bits become 0. Further, when RBs allocated to a terminal #2 are 3 and 15, the third and fifteenth bits in the bit map allocated to a terminal #2 are set to 1, and the other bits are set to 0. At this time, the order of bit columns of the bit map allocated to individual terminals is the same as the order of RBs. That is, the bit that represents the first RB becomes the first bit of the bit column.
When a radio resource is composed of NRB localized RBs, Equation 1 represents the number of bits needed for allocation information included in the map in order to allocate the radio resource to M mobile terminals in the bit-map method.XBitMap=M(LID+NRB+LTX)=M(LID+LTX)+M(NRB)  (Equation 1)
In this case, reference character XBITMAP indicates the number of bits needed for allocation information, reference character M indicates the number of mobile terminals allocated, reference character LID indicates bit lengths of IDs for discriminating mobile terminals, reference character NRB indicates the number of RBs, and reference character LTX indicates a bit length of a field to inform a transmission method.
As represented in Equation 1 described above, in order to represent the resource allocation information, in each mobile terminal, bits corresponding to the total number of RBs, bits for representing an ID of a mobile terminal, and bits for representing a transmission method are necessary. Therefore, as described above, the resource allocation method that uses the bit-map needs a large amount of bits.
FIG. 3 shows a method of allocating a radio resource composed of twenty-four distributed RBs to three mobile terminals. In this case, a base station informs each terminal of radio resource allocation information by using a run-length method.
When a frequency is not selectively used in a specific band, the radio resource can be sequentially allocated to each terminal by using the distributed RBs in a run-length method. In the run-length method, by using a size of the radio resource, the location of the radio resource allocated to each mobile terminal can be informed.
As shown in FIG. 3, in the case where the first to fourth RBs are allocated to the mobile terminal #1, if the terminal #1 recognizes that the terminal #1 is first allocated with the radio resource, that is, four RBs, the terminal #1 can know the location of the radio resource that is allocated to the terminal #1. Further, in the case of the terminal #2, if the terminal #2 knows that the number of RBs allocated to the terminal #2 is five and the four RBs are allocated to the terminal #1, the terminal #2 can know that the radio resource allocated to the terminal #2 corresponds to five RBs from 5 to 9. In the same manner, in the case of the terminal #3, if the terminal #3 can know the number of RBs allocated to the terminal #3 and the number of accumulated RBs of the radio resource allocated to the first and second terminals allocated with the radio resource prior to the terminal #3, the terminal #3 can know a starting point and an ending point of the radio resource that is allocated to the terminal #3.
As described above, when allocating a continuous radio resource, such as distributed RBs, to each mobile terminal in the run-length method, only the length of a radio resource allocated to each terminal is informed, and thus each terminal can know the location of the radio resource that is allocated to each terminal. Equation 2 represents the number of bits needed when informing each mobile terminal of radio resource allocation information in the case where the run-length method is used.XRunlength=XBitMap=M(LID+┌ log2NRB┐+LTX)  (Equation 2)
In this case, [X] indicates a minimal positive number that is equal to or larger than X, reference character XRunlength indicates the number of bits needed for allocation information, reference character M indicates the number of mobile terminals allocated, reference character LID indicates bit lengths of IDs for discriminating mobile terminals, reference character NRB indicates the number of RBs, and reference character LTX indicates a bit length of a field to inform a transmission method.
In the above-described run-length method, each mobile terminal needs to accurately know a size of the radio resource allocated to all of the mobile terminals allocated with the radio resource prior to each mobile terminal so as to calculate the location of the radio resource allocated to each terminal. However, in a mobile radio channel environment, all signals are not completely received. For this reason, when a previously allocated resource allocation message is not received or an error occurs at the time of receiving the resource allocation message, each terminal may mis-recognize the location of the radio resource allocated to each terminal. Accordingly, each mobile terminal does not receive a packet transmitted to each terminal through a downlink, and transmits a packet to an erroneous uplink wireless band.
Further, in the run-length method, when in a previous frame, a radio resource is allocated to a specific mobile terminal for a period of one frame or more or a specific RB is allocated in a fixed allocation method to be used until a message indicating stopping use of the specific RB is transmitted, each mobile terminal that confirms information for a radio resource allocated to each mobile terminal in a map of a current frame needs to accurately know all RBs that are allocated in the previous frame as well as a current frame and are valid until the current frame. However, when not accurately receiving the map of the previous frame, the previous allocated RBs cannot be discriminated by using the run-length information included in the map of the current frame, which does not accurately know the locations of the RBs allocated in the current frame.
Further, when the localized RB and the distributed RB are simultaneously allocated, in the run-length method, each mobile terminal needs to accurately know not only the distributed RBs allocated to the other mobile terminals but also the locations of the localized RBs so as to know the locations of the RBs allocated to each mobile terminal. Furthermore, when using a plurality of sub-maps using different modulation and coding schemes in order to transmit allocation information, each mobile terminal needs to accurately receive not only a sub-map including allocation information corresponding to each mobile terminal but also other sub-maps including allocation information corresponding to the other terminals. However, in the case where an error occurs when each mobile terminal receives other sub-maps, each mobile terminal cannot accurately know the location of the radio resource that is allocated to each mobile terminal.
Accordingly, even in the case where the distributed RBs are allocated, in order to accurately inform the location of the radio resource that is allocated to each mobile terminal, each terminal needs to know a radio resource allocated to each mobile terminal by using a bit-map method or a start-length method regardless of allocations for the other mobile terminals.
FIG. 4 shows the resource allocation using the bit-map method in the case where the localized RB and the distributed RB are simultaneously allocated and a specific RB is used in a state where the specific PB is reserved until a current frame from a previous frame.
As shown in FIG. 4, the first, sixth, eighth, and thirteenth RBs are reserved in the previous frame, and the second, third, fifth, ninth, fourteenth, fifteenth, and seventeenth RBs indicate the localized RBs. Meanwhile, except for the reserved RBs and the RBs allocated as the localized RBs, the other RBs are allocated and used as the distributed RBs.
As shown in FIG. 4, due to using the previously reserved RBs and the localized RBs, the allocations of the distributed RBs are not continuously made but are distributed. Therefore, the bit-map method is used with respect to the distributed RBs. As such, when the allocation information is represented in the bit-map method for the distributed RBs, bit columns each having a length corresponding to the number of RBs in the entire radio resource are needed by the number of mobile terminals, and thus the size of the map for representing the allocation information is increased.
FIG. 5 shows a case where a bit-map method is used for localized RBs and a start-length method is used for distributed RBs in the allocation of the radio resource having the same RB structure as FIG. 4. The start-length method is a method in which a starting location of the radio resource allocated to each terminal and the number of allocated RBs are included in the map.
As shown in FIG. 5, when constructing radio resource allocation information, the number of bits required is decreased, as compared with the bit-map method shown in FIG. 4. However, in regards to the RBs to be not continuous but distributed, the RBs need to be informed of the independent start-length. Therefore, the number of start lengths is needed by the number of distributed RBs, and thus the size of the map is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.